In semiconductor devices including both transistor cells and a diode functionality such as MCDs (MOS controlled diodes) and RC-IGBTs (reverse conducting insulated gate bipolar transistors), mobile charge carriers flood a semiconductor region along a forward biased pn junction and form a dense charge carrier plasma resulting in a low forward resistance of the diode. When the concerned pn junction commutates thereby changing from forward biased to reverse biased, a reverse recovery current removes the charge carrier plasma. The reverse recovery current contributes to dynamic switching losses of the semiconductor device. Typically, in a desaturation period preceding the change of the pn junction from forward biased to reverse biased a gated MOS channel attenuates the charge carrier plasma in order to reduce the dynamic switching losses. A safety period between the end of the desaturation period and the beginning of the commutation secures that the semiconductor device is in a blocking mode with closed MOS channel before commutation starts. During the safety period the charge carrier plasma partially recovers and foils to some degree the desaturation mechanism.
It is desirable to improve the switching characteristics of semiconductor devices including transistor cells as well as a diode functionality.